Bovine herpesvirus 5 (BoHV5) subtype b is unexpectedly a recombinant virus between BoHV5 and BoHV1, the agent of infectious bovine rhinotracheitis

SILVINA S. MAIDANA; AXEL MAUROY; ETIENNE THIRY; SONIA A. ROMERA

Congreso; World Buiatrics Congress; 2016

Objectives: Bovine herpesvirus 5 (BoHV5) is the agent of bovine encephalitis occurring especially in South America,together with BoHV1, responsible for infectious bovine rhinotracheitis (IBR). Among the 3 BoHV5 subtypes, subtype ?b?was until now only detected in Argentina, and seems to be less prevalent. Both BoHV1 and BoHV5 belong to ruminant alphaherpesviruses and share a high genetic similarity. Under experimental conditions, we obtained interspecies recombinants between the involved viruses, BoHV1 and BoHV5. We report here for the first time the identification of homologous recombination between BoHV1 and BoHV5 in field virus isolates.Materials and Methods: Two fragments of the three BoHV5b isolates were amplified by PCR, then sequenced and a phylogenetic inference was performed using the MEGA version 4 software package. Tree topology was constructed by maximum composite likelihood method with the Tamura and Nei model (1000 replicate bootstrap values). After we amplified by PCR the complete UL27 gene of three BoHV5b isolates, sequenced and genetic recombination was analysed using a sliding-window genetic diversity plot (Simplot software version 3.5.1 available at http://sray.med.som.jhmi.edu/SCRoftware) and the Recombinant Detection Program (RDP), version 3, available at http://darwin.uvigo.es/rdp/ rdp.html).Results: We showed by phylogenetic analyses that these three BoHV5b isolates clustered differently with BoHV1 and BoHV5 depending on the genes encoding glycoprotein B (gB) or D (gD) suggesting that these viruses could be recombinants between BoHV1 and BoHV5. We detected two recombination breakpoints located in the long unit (UL)genomic region within the UL27 gene open reading frame. Based on the BoHV5 UL27 gene (GenBank accession number YP003662497.1) one recombination breakpoint extended from the nucleotide (nt) 475 to nt 491 and the other one from2749 nt to 2761 nt giving a recombination fragment of 2286 base pairs showing 100% nucleotidic identity with the BoHV1.2b subtype genome. Other genomic regions, encompassing five gene fragments from UL and two from the short unit (US) region, were also analyzed by PCR and sequencing, resulting in 100% nucleotide identity with the subtype BoHV5a genome.Conclusions: Homologous recombination between two related ruminant alphaherpesviruses was shown in natural field conditions. We found three recombinant field isolates between BoHV1 and BoHV5, previously known as BoHV5b subtype. The existence of natural recombination and also the co-circulation of different ruminant alphaherpesviruses increase the complexity to carry on programs of control and eradication of IBR.Especially their impact on BoHV1 differential diagnosis methods and the risk to escape vaccine-induced immunity depending on the degree of antigenic variation caused by recombination should now be taken into account.